Heretofore, electrophotography used an image-forming method in copying machines comprising the following steps to provide uniform electric charge on a photoreceptor comprising a light-sensitive layer made of a photoconductive material,
a step of forming an electrostatic latent image corresponding to an original image by imagewise exposure on the surface of said photoreceptor;
a step of forming a toner image developed with developer" and
a step of transferring this toner image onto a recording material such as a paper sheet and, thereafter, a step of fixing the toner image on to the recording material.
For the developer, a variety of functions are required to perform developability or fixing. Particularly, in light of electrophotographic mechanism, it is important to provide electrification property to a toner. As a method of controlling electrification on the toner, a method of adding charge controlling agents to a toner have been known in the art.
Conventionally, the above-mentioned charge controlling agents had been added inside the toner particles and used as a material capable of controlling electrification of the toner particles. On the ether hand, the charge controlling agent is controlled to be present on the surface of the toner particles, so that attempts have been made to control electrification of the toner particles. In this technology, since the charge controlling agent is present and exposed on the surface of the toner particles, it can be performed with certainty to control frictional electrification. However, when the charge controlling agent is present only on the surface of the toner particles, electrification may easily be controlled, yet of electrification stability tends to be lowered, Thus, in Japanese Patent O.P.I. Publication No.21862(1992), it has proposed that the existence of the charge controlling agent both inside and on the surface of the toner particles is needed in order that the toner particles show excellent electrification controlling property and excellent electrification stability.
On the other hand, as for the carrier, which functions to provide electric charges on to the toner particles, use of a resin-coated carrier has been the main stream in the art in light of durability and image qualities, particularly including reproduction performance of fine lines. However, when the images are formed repeatedly, due to wearing and peeling-off of the coating resin, core magnetic particle comes to be exposed on the carrier surface, and a result, electrification providing effect of the carrier to the toner particles is remarkably lowered, which often causes background fogging due to lowering of electrification and scattering of the toner particles in the copying machine. Further, a so called toner spent phenomenon, in which some of the toner constituents adhere to the surface of the carrier particles, is accelerated. Particularly, when toner containing a charge controlling agent is used, contamination of the carrier by the charge controlling agent can be a major problem.
Therefore, the object of the present invention is to provide a developer for electrophotography, with which stable frictional electrification performance can be maintained without causing fogging or toner scattering and, thus, toner images with good image qualities, can be obtained, and realized a method of development by the use of the same.